Boneitis seems to be an extreme and accelerated form of rheumatism. If so, it could be treated easily with a number of disease-modifying antirheumatic drugs in combination with anti-inflammatories (like NSAIDs); both of which, ironically, exist in the 21st century. This would mitigate That Guy's need for a trip to the 31st century in the first place. On the other hand, if it is a dystrophic disorder as it is portrayed, there is currently no known cure - in which case his trip would be legitimized.